The present invention relates to a refrigeration system for containers, particularly for railroad box cars. Such railcars, sometimes referred to as "reefers", are used to transport fresh or frozen foods in a cold or frozen state. This invention particularly relates to using CO .sub.2 snow to keep the cargo cold by placing the CO .sub.2 snow in an attic or bunker located above the cargo area of the container and providing vents through the bunker to allow the CO.sub.2 gas generated by the sublimation of the CO.sub.2 snow to fall downwardly into the cargo area to cool the load.
Cryogenically cooled box cars have been disclosed in U.S. Pat. Nos. 4,891,954; 4,704,876; 4,593,536; 4,761,969; and British Pat. No. 399,678. In all of these patents, CO.sub.2 in solid form is located above the cargo area in a bunker wherein the sublimated CO.sub.2 gas is allowed to fall downwardly into the cargo area to cool the load.
The '954 and '876, '536 and '969 patents all disclose corrugated floors to allow the downwardly flowing CO.sub.2 gas to proceed beneath the load to ensure cooling. The latter named three patents also disclose corrugated walls for providing a vertical pathway for the downward flowing CO.sub.2 gas to flow between the cargo and the walls to reach the floor.